Cellulose-ester dope or varnish.



UNITED STATES PATENT OFFICE.

JOHN NAISHGOLDSMITH, 0F HOLBORN, LONDON, ENGLAND, ASSIGNOR TO THE BRITISH EMAILLITE COMPANY, LIMITED, 0F PICGADILLY CIRCUS, LON'DON, ENGLAND.

CELLULOSE-ESTER DOPE OR VARNISH.

No Drawing.

. tion.

This invention relates to the manufacture of dopes of the kind used for coating the surfaces of aeroplanes, and its chief objects are to improve the adhesiveness, strength 1 and surface of the coating and to reduce or eliminate the poisonous or deleterious properties of dopes. Dopes as at present employed consist broadly of solutions of cellulose esters, especially the acetate, in such solvents as acetone, tetrachlorethane, ketone, methylated spirit and benzene, usually with a small proportion of triphenyl phosphate, added with the object of reducing the inflammability. Aeroplane dopes must produce in and on the fabric em loyed an elastic highly contractile, film wlth a hard surface which when struck must yield a 7 clear resonant note (an indication that the necessar, contraction has been obtained) with s cient body and rigidity (obtained by a succession of coats) to retain its stream line contour during flight.

According to this invention I add to a cellulose ester dope prepared so as to produce a film having the above characteristics a proportion of acetanilid or a mixture of acetanilid and triacetin, amounting preferably, for ordinary aeroplane purposes, to form about 5 to about 40 per cent. by weight (or for special purposes up to about 100 per cent.) of the cellulose ester. The ratio of triacetin to acetanilid in the mixture of these two substances may vary from about 1:5 to 3:2 for general purposes. When the triacetin much exceeds the acetanilid the dope films are less resistant to weathering. The resistance of these dope films to the weather is also. influenced by the substances already mentioned as generally employed in dopes. Q

The above stated ingredients (acetanilid or a mixture of acetanilid and triacetin) are found to give in the dope properties hitherto obtained only by the use of tetrachlorethane, or an equivalent chlorinated hydrocarbon Specification of Letters Patent. Patented luar, 25, 1919, Application filed June 13, 1917. Serial No. 174,545. r I

which is generally used in large quantities,

lid singly the tetrachlorethane may be com-' pletely eliminatedand the dope thus rendered harmless to the persons engaged in manufacturing or applying it. A bloom or efllorescence which is harmless in nature is found to be developed by the use' of the .acetanilid addition only, but this .is not found with the acetanilid-triacetin mixture.

With regard to the proportions of triacetin and acetanilid to the cellulose ester the desired characteristics of the dope have to be considered. Where a rapid tightening effect on the doped fabric is the chief object, 5 to 10 per cent. of acetanilid alone or of the mixture is suflicient, but for general purposes the most desirable percentages (taking the cellulose ester as the standard of measurement) are higher, for example, about 13 per cent. of acetanilid with 17 per cent. of triacetin, making 30 per cent. of the mixture, or 25 per cent. of acetanilid alone.

Where a less rigid effect is desired, for instance for a later or final coating, a higher percentage of the ingredient or ingredients maybe used, say, about 40 per cent. for a moderate increase of pliability while experience has shown that a durable and pliable film is obtained with even up to 100 per cent., for special purposes, such as the finishing coats of aeroplanes, 25 per cent. of

acetanilid with 17 per cent. of triacetin mayweight of cellulose ester present in the dope.

The proportions of the solvents employed may therefore vary considerably but the examples given below. contain proportions suitable for ordinary purposes Cellulose acetate 21 grams. Triphenyl phosphate 1. 8 grams. Acetone l c. c. Triacetin 3 c. c. Acetanilid- 1' 2. 7 grams.-

Cellulose acetate 21 grams. Triphenyl phosphate 3 grams. Methyl acetone 100 c. 0. Methyl ethyl ketone 150 c. c. Acetanilid 5 grams.

Methyl acetone is a commercial mixture of acetone, methyl alcohol and methyl acetate) memes Cellulose acetate 22 grams. Methyl acetone 150 c 0. Methyl ethyl ketone 25 c. c. Benzol 75 c. c. 'Triacetin 3 c. c Acetanilid 2.5 grams. 4.

- (As an example of a less rigid dope). Cellulose acetate 21 grams Triphenyl phosphate 2. 7 grams. Methyl acetone 100 c. 0. Methyl ethyl ketone 150 c. c. Triacetin 8 c. c. Acetanilid 10 grams.

When acetanilid with or without triacetin is used according to this invention it may be employed in conjunction with other camvphor substitutes and with solvents other than those specifically mentioned, which are given merely as examples.

What I claim and desire to ters Patent of the United States is g l. A cellulose ester dope of the kind set forth, containing a small proportion of acetanilid and triacetin for the purpose specified.

2. A cellulose ester dope of the kind set forth containing acetanilidor a mixture of acetanilid and triacetin amounting to from .5 to about 100 per cent. of the cellulose ester.

JOHN NAISH GOLDSMITH.

secure by Let- 2 

